Force storing GC state until we see a labeled IG (#114475)

* Force storing GC state until we see a labelled IG

* review feedback

Author: kunalspathak

src/coreclr/jit/emit.cpp

@@ -1008,7 +1008,13 @@ insGroup* emitter::emitSavIG(bool emitAdd)
         emitPrevGCrefRegs = emitThisGCrefRegs;
         emitPrevByrefRegs = emitThisByrefRegs;
 
-        emitForceStoreGCState = false;
+        if (emitAddedLabel)
+        {
+            // Reset emitForceStoreGCState only after seeing label. It will keep
+            // marking IGs with IGF_GC_VARS flag until that.
+            emitForceStoreGCState = false;
+            emitAddedLabel        = false;
+        }
     }
 
 #ifdef DEBUG
@@ -1277,6 +1283,7 @@ void emitter::emitBegFN(bool hasFramePtr
     emitPrevByrefRegs = RBM_NONE;
 
     emitForceStoreGCState = false;
+    emitAddedLabel        = false;
 
 #ifdef DEBUG
 
@@ -2839,6 +2846,8 @@ void* emitter::emitAddLabel(VARSET_VALARG_TP GCvars, regMaskTP gcrefRegs, regMas
         }
     }
 
+    emitAddedLabel = true;
+
     /* Create a new IG if the current one is non-empty */
 
     if (emitCurIGnonEmpty())

src/coreclr/jit/emit.h

@@ -2761,6 +2761,14 @@ class emitter
 
     bool emitForceStoreGCState;
 
+    // This flag is used together with `emitForceStoreGCState`. After we set
+    // emitForceStoreGCState = true, we will mark `emitAddedLabel` to true whenever
+    // we see a label IG. In emitSavIG, we will reset `emitForceStoreGCState = false`
+    // only after seeing `emitAddedLabel == true`. Until then, we will keep recording
+    // GC_VARS on the IGs.
+
+    bool emitAddedLabel;
+
     // emitThis* variables are used during emission, to track GC updates
     // on a per-instruction basis. During code generation, per-instruction
     // tracking is done with variables gcVarPtrSetCur, gcRegGCrefSetCur,